linux-kernel - Re: [PATCH v2 02/10] PCI/LUO: Create requested liveupdate device list

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Message-ID: <CAF8kJuN2-Y7YZkY5PrerK=AdTUfsaX0140-yJJSTnNORucYfqQ@mail.gmail.com>
Date: Mon, 29 Sep 2025 19:13:51 -0700
From: Chris Li <chrisl@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>, Len Brown <lenb@...nel.org>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>, Pasha Tatashin <tatashin@...gle.com>, 
	Jason Miu <jasonmiu@...gle.com>, Vipin Sharma <vipinsh@...gle.com>, 
	Saeed Mahameed <saeedm@...dia.com>, Adithya Jayachandran <ajayachandra@...dia.com>, 
	Parav Pandit <parav@...dia.com>, William Tu <witu@...dia.com>, Mike Rapoport <rppt@...nel.org>, 
	Leon Romanovsky <leon@...nel.org>
Subject: Re: [PATCH v2 02/10] PCI/LUO: Create requested liveupdate device list

On Mon, Sep 29, 2025 at 10:47 AM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> On Tue, Sep 16, 2025 at 12:45:10AM -0700, Chris Li wrote:
> >  static int pci_liveupdate_prepare(void *arg, u64 *data)
> >  {
> > +     LIST_HEAD(requested_devices);
> > +
> >       pr_info("prepare data[%llx]\n", *data);
> > +
> > +     pci_lock_rescan_remove();
> > +     down_write(&pci_bus_sem);
> > +
> > +     build_liveupdate_devices(&requested_devices);
> > +     cleanup_liveupdate_devices(&requested_devices);
> > +
> > +     up_write(&pci_bus_sem);
> > +     pci_unlock_rescan_remove();
> >       return 0;
> >  }
>
> This doesn't seem conceptually right, PCI should not be preserving
> everything. Only devices and their related hierarchy that are opted
> into live update by iommufd should be preserved.

Can you elaborate? This is not preserving everything, for repserveding
bus master, only the device and the parent PCI bridge are added to the
requested_devies list. That is done in the
build_liveupdate_devices(), the device is added to the listhead pass
into the function. So it matches the "their related hierarchy" part.
Can you explain what unnecessary device was preserved in this?

It is not using iommufd, just the dev->lu.flags flags, the flags are
set when VFIO adds a device to VM. Here the PCI LU test driver just
adds the flag in the probe function to simulate that VFIO ioctl.

Iommufd is a separate series, not this one.

Chris


Chris